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Elastomers
Kinds of Elastomers Terms modified by Elastomers Selected AbstractsOn Toughness and Stiffness of Poly(butylene terephthalate) with Epoxide-Containing Elastomer by Reactive ExtrusionMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2004Zhong-Zhen Yu Abstract Summary: To obtain a balance between toughness (as measured by notched impact strength) and elastic stiffness of poly(butylene terephthalate) (PBT), a small amount of tetra-functional epoxy monomer was incorporated into PBT/[ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E-MA-GMA)] blends during the reactive extrusion process. The effectiveness of toughening by E-MA-GMA and the effect of the epoxy monomer were investigated. It was found that E-MA-GMA was finely dispersed in PBT matrix, whose toughness was significantly enhanced, but the stiffness decreased linearly, with increasing E-MA-GMA content. Addition of 0.2 phr epoxy monomer was noted to further improve the dispersion of E-MA-GMA particles by increasing the viscosity of the PBT matrix. While use of epoxy monomer had little influence on the notched impact strength of the blends, there was a distinct increase in the elastic stiffness. SEM micrographs of impact-fracture surfaces indicated that extensive matrix shear yielding was the main impact energy dissipation mechanism in both types of blends, with or without epoxy monomer, and containing 20 wt.-% or more elastomer. SEM micrographs of freeze-fractured surfaces of PBT/E-MA-GMA blend illustrating the finer dispersion of E-MA-GMA in the presence of epoxy monomer. [source] Polymer Matrix Nanocomposites from Biodegradable Thermoplastic Elastomers,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Miroslawa El Fray Soft and elastomeric poly(ester,ether,ester) multiblock terpolymers were synthesized in presence of 0.5 wt % hydroxyapatite (HAp) nanoparticles to form nanocomposites. The addition of sintered HAp particles enhanced cell proliferation and diminished the number of dead and apoptotic cells. Implantation tests indicated that the observed hard tissue changes led to intense bone remodeling (see picture) [source] Improved Microcontact Printing of Proteins using Hydrophilic Thermoplastic Elastomers as Stamp Materials,ADVANCED ENGINEERING MATERIALS, Issue 12 2007C. Trimbach Recently, the microstructuring of biological species, such as proteins, using microcontact printing (,CP), has become very popular. Microstructuring of proteins is useful for a variety of applications, such as biosensors, controlled cell growth and adhesion and microarrays for bioanalytical detection. Here the authors investigated the microcontact printing of proteins using a hydrophilic thermoplastic elastomeric stamp material. The emphasis is placed on the quality of the printed patterns with respect to inking time and protein concentration in the ink. [source] Advances and Applications of Biodegradable Elastomers in Regenerative MedicineADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Maria Concepcion Serrano Abstract When elastomers were first proposed as useful materials for regenerative medicine a few decades ago, their high versatility and suitability for a diverse and wide range of in vivo applications could not have been predicted. Due to their ability to recover after deformation, these materials were first introduced in tissue engineering in an attempt to mimic the mechanical properties of the extracellular matrix. Furthermore, elastomeric characteristics have been described as important criteria for cell interaction by modulating cellular behavior. From soft to hard tissues, elastomers have demonstrated degradation, mechanical, and biocompatibility requirements in accordance with the target tissue. In this feature article, biodegradable synthetic polyester elastomers that have been reported in the literature are discussed, with special focus on those that show promise for in vivo tissue replacement. Their satisfactory performance in vivo shows the promise of elastomers for use in regenerative medicine. However, further investigation is required to demonstrate the prospect of elastomer-based therapies in clinical trials. [source] Metal Ion Implantation for the Fabrication of Stretchable Electrodes on ElastomersADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Samuel Rosset Abstract Here, the use of low-energy metal ion implantation by filtered cathodic vacuum arc to create highly deformable electrodes on polydimethylsiloxane (PDMS) membranes is reported. Implantation leads to the creation of nanometer-size clusters in the first 50,nm below the surface. When the elastomer is stretched, these small clusters can move relative to one another, maintaining electrical conduction at strains of up to 175%. Sheet resistance versus ion dose, resistance versus strain, time stability of the resistance, and the impact of implantation on the elastomer's Young's modulus are investigated for gold, palladium, and titanium implantations. Of the three tested metals, gold has the best performance, combining low and stable surface resistance, very high strain capabilities before loss of electrical conduction, and low impact on the Young's modulus of the PDMS membrane. These electrodes are cyclically strained to 30% for more than 105 cycles and remain conductive. In contrast, sputtered or evaporate metals films cease to conduct at strains of order 3%. Additionally, metal ion implantation allows for creating semi-transparent electrodes. The optical transmission through 25-µm-thick PDMS membranes decreases from 90% to 60% for Pd implantations at doses used to make stretchable electrodes. The implantation technique presented here allows the rapid production of reliable stretchable electrodes for a number of applications, including dielectric elastomer actuators and foldable or rollable electronics. [source] Silicone,Poly(hexylthiophene) Blends as Elastomers with Enhanced Electromechanical Transduction Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2008F. Carpi Abstract Dielectric elastomers are progressively emerging as one of the best-performing classes of electroactive polymers for electromechanical transduction. They are used for actuation devices driven by the so-called Maxwell stress effect. At present, the need for high-driving electric fields limits the use of these transduction materials in some areas of potential application, especially in the case of biomedical disciplines. A reduction of the driving fields may be achieved with new elastomers offering intrinsically superior electromechanical properties. So far, most attempts in this direction have been focused on the development of composites between elastomer matrixes and high-permittivity ceramic fillers, yielding limited results. In this work, a different approach was adopted for increasing the electromechanical response of a common type of dielectric elastomer. The technique consisted in blending, rather than loading, the elastomer (poly(dimethylsiloxane)) with a highly polarizable conjugated polymer (undoped poly(3-hexylthiophene)). The resulting material was characterised by dielectric spectroscopy, scanning electron microscopy, tensile mechanical analysis, and electromechanical transduction tests. Very low percentages (1,6 wt %) of poly(3-hexylthiophene) yielded both an increase of the relative dielectric permittivity and an unexpected reduction of the tensile elastic modulus. Both these factors synergetically contributed to a remarkable increase of the electromechanical response, which reached a maximum at 1 wt % content of conjugated polymer. Estimations based on a simple linear model were compared with the experimental electromechanical data and a good agreement was found up to 1 wt %. This approach may lead to the development of new types of materials suitable for several types of applications requiring elastomers with improved electromechanical properties. [source] A Continuous Flow Synthesis of Micrometer-Sized Actuators from Liquid Crystalline ElastomersADVANCED MATERIALS, Issue 47 2009Christian Ohm We demonstrate the use of a microfluidic setup to prepare monodisperse and spherical beads from a liquid crystalline elastomer. These particles show a strong and reversible shape change into a cigar-like conformation during the transition into the isotropic phase. These properies are a result of the monodomainic alignment of the mesogens in the flow field of the microfluidic setup. [source] Calamitic Liquid-Crystalline Elastomers Swollen in Bent-Core Liquid-Crystal SolventsADVANCED MATERIALS, Issue 16 2009Martin Chambers The swelling of calamitic liquid crystal elastomers (LCEs) with bent-core mesogens is investigated in the isotropic phase of both materials. The swelling magnitude and dynamics are determined and fitted with a dual exponential. The host LCEs imbibe bent-core molecules up to 30, 40 mol%. The swollen elastomers exhibit nematic phases, with some possessing a lower temperature smectic phase. [source] Biomedical Materials: Nanoporous Biodegradable Elastomers (Adv. Mater.ADVANCED MATERIALS, Issue 2 20092/2009) The mechanical properties and degradation rate of elastomers can be tailored with nanoporosity. The elastomers described in this study by Guillermo Ameer and co-workers (p. 188) are based on citric acid and are biocompatible. The nanopores also facilitate the entrapment and slow release of macromolecular therapeutics. The inside cover depicts the nano- and microarchitecture of the elastomer prior to pore collapse. [source] Lipase-Catalyzed Synthesis and Properties of Poly[(12-hydroxydodecanoate)- co -(12-hydroxystearate)] Directed towards Novel Green and Sustainable ElastomersMACROMOLECULAR BIOSCIENCE, Issue 1 2008Hiroki Ebata Abstract Novel green and sustainable elastomers having both good biodegradability and chemical recyclability properties were designed and synthesized using potentially biobased materials and lipase as an environmentally benign catalyst. High molecular weight poly[(12-hydroxydodecanoate)- co -(12-hydroxystearate)] [poly(12HD- co -12HS)] samples with varying monomer ratios were prepared by the polycondensation of 12-hydroxydodecanoic acid and methyl 12-hydroxystearate using immobilized lipase from Candida antarctica (IM-CA) in toluene in the presence of molecular sieves 4A at 90,°C. Although poly(12HD) is a highly crystalline polyester having a melting temperature (Tm) of 87.6,°C and crystalline temperature (Tc) of 64,°C, by the copolymerization of 12HD with 12HS, both the Tm and Tc of the copolymer decreased with increasing 12HS contents, and poly(12HD- co -12HS) containing more than 60 mol-% 12HS was a viscous liquid at room temperature. At the same time, the Young's modulus and hardness also decreased with increasing 12HS content, and poly(12HD- co -36 mol-% 12HS) exhibited an elastic behavior, having a hardness of 70 A using a durometer A. In addition, it showed an excellent biodegradability by activated sludge and chemical recyclability by lipase. [source] Investigation of Soft Component Mobility in Thermoplastic Elastomers using Homo- and Heteronuclear Dipolar Filtered 1H Double Quantum NMR ExperimentsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2004Marko Bertmer Abstract Summary: Information about segmental mobility in thermoplastic elastomers was obtained using static 1H double quantum (DQ) NMR experiments in combination with homo- and heteronuclear dipolar filters, e.g. 13C editing of 1H DQ buildup curves. Block copolymers of poly(butylene terephthalate) (PBT) as hard blocks and poly(tetramethylene oxide) (PTMO) as soft blocks (PBT- block -PTMO) were investigated by varying composition and block length. By simulation of the DQ buildup curves, residual dipolar couplings and with this the average order parameter were deduced for the mobile PTMO blocks which are sensitive to the segmental mobility responsible for the viscoelastic properties of thermoplastic elastomers. A strong correlation exists between residual dipolar coupling and composition. Furthermore, the average order parameter correlates linearly with the amount of PTMO in a PTMO-rich phase as determined in previous studies. Additionally, 1H transverse magnetization relaxation measurements revealed a direct correlation between the effective T2 relaxation time of the soft domain and the composition of the thermoplastic elastomers. Correlation of the average order parameter vs. the fraction of PTMO in the PTMO-rich phase. [source] Deformation Behavior of PET, PBT and PBT-Based Thermoplastic Elastomers as Revealed by SAXS from SynchrotronMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2003Norbert Stribeck Abstract The present paper discloses the changes in the nanostructure as revealed by small-angle X-ray scattering (SAXS) of synchrotron radiation of anisotropic semi-crystalline samples of polyester and poly(ether ester) type differing in their chemical composition, while subjected to controlled progressive elongation. From the group of polyesters poly(ethylene terephthalate) (PET), and poly(butylene terephthalate) (PBT) were selected. Two PBT-based commercial poly(ether ester)s were also studied differing in the molecular weight of their soft segments (poly(tetramethylene glycol), PTMG) being 1000 and 2000, respectively. A blend of PBT and EM550 (40/60 by wt.) was also characterized. All materials underwent the same sample preparation process resulting in highly oriented "bristles" of 1 mm diameter. It was found that ,b, the elongation at break, strongly depends on the flexibility of the glycol residues of the materials studied , ranging from ,b,=,8% for PET that contains ethylene glycol residues, through ,b,=,18% for PBT including the more flexible tetramethylene glycol (TMG) up to ,b,=,510% for the PEE containing the longest PTMG moieties. During straining the relationship between the external elongation , and the changes in the long spacing L was determined. After relaxation from each deformation step the relationship between the tensile set ,r and the long period L was also followed and discussed. Such analysis led to a model describing the nanostructure evolution during the deformation-relaxation cycle that finally was verified and refined utilizing the multidimensional chord distribution function computed from the anisotropic SAXS patterns. 2D SAXS patterns (pseudo color) of bristles of PET (PBT), respectively, cold drawn, ,,=,3.5 (,,=,2.3) and annealed with fixed ends for 6 h at 240,°C (180,°C), recorded at room temperature at a forced tensile deformation , or tensile set (residual elongation) ,r in percent. [source] The Role of Filler Networking in Fatigue Crack Propagation of Elastomers under High-Severity ConditionsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2009Manfred Klüppel Abstract Structural parameters of the filler network have been evaluated by fitting quasi-static stress/strain cycles to the dynamic flocculation model. It is found that the size of filler clusters as well as the strength of filler,filler bonds increase with filler loading and carbon black activity (specific surface). This correlates with the behavior of the tear resistance obtained for pulsed loading under high-severity conditions, implying that the characteristics of the filler network govern the fracture properties of filled elastomers. The behavior of the power law exponent of fatigue crack propagation versus tearing energy can be explained by flash temperature effects in the crack tip area. [source] Phase Biaxility in Smectic-A Side-Chain Liquid Crystalline ElastomersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2009Rebekka Storz Abstract 2H NMR investigations on the biaxial phase behavior of smectic-A liquid crystalline side-chain elastomers are presented. Biaxiality parameters were determined by measuring the quadrupolar splitting of two spin probes, namely benzene-d6 and hexamethylbenzene-d18, at various angles between the principal director and the external magnetic field: while for a uniaxial sample the angular dependence can be described by the second Legendre polynomial, an additional asymmetric term needs to be included to fit the data of the two investigated biaxial systems. Two elastomers synthesized from mesogens that differ in the molecular geometry in order to study the molecular origin of biaxiality were compared. Biaxiality is observed for both elastomers when approaching the glass transition, suggesting that the network dynamics dominate the formation of the biaxial phase. [source] Filler networks in elastomersMACROMOLECULAR SYMPOSIA, Issue 1 2003Françoise Ehrburger-Dolle Abstract Elastomers are soft materials that can be reinforced by dispersing into them nanosized solid particles. Common examples of the latter are silica or carbon black aggregates. However, the mechanism of reinforcement is still not yet fully understood. Our work consists in investigating by small-angle X-ray scattering (SAXS) the structure of the aggregate network spreading throughout the matrix in the initial sample and its modification during and after straining (elongation). The goal is to relate the macroscopic mechanical behaviour with the structure of the aggregate network. The present paper is a qualitative overview of recent results obtained on well defined composites. [source] Novel Segmented Thermoplastic Polyurethanes Elastomers Based on Tetrahydrofuran Ethylene Oxide Copolyethers as High Energetic Propellant BindersPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2003Fu-Tai Chen Abstract Novel thermoplastic polyurethane (TPU) elastomers based on copolyether (tetrahydrofuran ethylene oxide) as soft segments, isophorone diisocyanate and 1,4-butanediol as hard segments were synthesized for the purpose of using as propellant binders. In order to increase the miscibility of thermoplastic polyurethane elastomers with nitrate ester, polyethylene glycol (PEG) is incorporated in the co-polyether (tetrahydrofuran ethylene oxide) as soft segment. When the molecular weight and content of polyethylene glycol are controlled to 4000 and 6% of soft segments, respectively, the properties of thermoplastic polyurethane elastomers are most perfect. If plasticizing ratio of nitrate ester to thermoplastic polyurethane elastomers exceeds 4 no crystallinities are determined at room temperature. The propellant samples were prepared by a conventional absorption-rolling extrusion process and the mechanical and combustion properties evaluated afterwards. The maximum impulse reaches up to 265,270 s which is a little bit higher than that of a HTPB propellant. The measured results reveal a promising TPE propellant candidate which shows good processing temperature (<393,K) and excellent mechanical properties. An attracting feature which can be pointed out is that the burning rate pressure exponent reaches as low as 0.36 without the addition of burning rate catalysts. This enables an easy control of propellant combustion. [source] A Review of the Biologic Effects, Clinical Efficacy, and Safety of Silicone Elastomer Sheeting for Hypertrophic and Keloid Scar Treatment and ManagementDERMATOLOGIC SURGERY, Issue 11 2007BRIAN BERMAN MD Silicone elastomer sheeting is a medical device used to prevent the development of and improve the appearance and feel of hypertrophic and keloid scars. The precise mechanism of action of silicone elastomer sheeting has not been defined, but clinical trials report that this device is safe and effective for the treatment and prevention of hypertrophic and keloid scars if worn over the scar for 12 to 24 hours per day for at least 2 to 3 months. Some of the silicone elastomer sheeting products currently on the market are durable and adhere well to the skin. These products are an attractive treatment option because of their ease of use and low risk of adverse effects compared to other treatments, such as surgical excision, intralesional corticosteroid injections, pressure therapy, radiation, laser treatment, and cryotherapy. Additional controlled clinical trials with large patient populations may provide further evidence for the efficacy of silicone elastomer sheeting in the treatment and prevention of hypertrophic and keloid scars. The purpose of this article is to review the literature on silicone elastomer sheeting products and to discuss their clinical application in the treatment and prevention of hypertrophic and keloid scars. [source] A mathematical hysteretic model for elastomeric isolation bearingsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2002J. S. Hwang Abstract An analytical model for high damping elastomeric isolation bearings is presented in this paper. The model is used to describe mathematically the damping force and restoring force of the rubber material and bearing. Ten parameters to be identified from cyclic loading tests are included in the model. The sensitivity of the ten parameters in affecting the model is examined. These ten parameters are functions of a number of influence factors on the elastomer such as the rubber compound, Mullins effect, scragging effect, frequency, temperature and axial load. In this study, however, only the Mullins effect, scragging effect, frequency and temperature are investigated. Both material tests and shaking table tests were performed to validate the proposed model. Based on the comparison between the experimental and the analytical results, it is found that the proposed analytical model is capable of predicting the shear force,displacement hysteresis very accurately for both rubber material and bearing under cyclic loading reversals. The seismic response time histories of the bearing can also be captured, using the proposed analytical model, with a practically acceptable precision. Copyright © 2002 John Wiley & Sons, Ltd. [source] Influence of TiO2 Nanoparticles Incorporated into Elastomeric Polyesters on their Biocompatibility In Vitro and In VivoADVANCED ENGINEERING MATERIALS, Issue 11 2009Miroslawa El-Fray Abstract Fibroblasts proliferation and apoptosis as well as tissue response after implantation of elastomers containing nanocrystalline TiO2 were investigated in the present in vitro and in vivo study. Materials investigated were soft poly(aliphatic/aromatic-ester) multiblock thermoplastic elastomers with poly(ethylene terephthalate) (PET) hard segments and dimerized linoleic acid (DLA) soft segments, respectively, containing 0.2,wt% TiO2 nanoparticles. An investigation of the influence of TiO2 nanoparticles incorporated into polymeric material on in vitro biocompatibility revealed enhanced cell proliferation and diminished number of necrotic and apoptotic cells as compared to nanoparticles-free polymer. Implantation tests indicated that the observed tissue changes were similar to those observed with medical-grade silicone elastomer, no evidence of contact necrosis being observed. The unchanged morphology of rat liver hepatocytes and the lack of parenchymal necrosis also indicated that exposure to the material containing TiO2 nanoparticles, did not cause any cytotoxic reactions. The present study, thus, showed that elastomeric polyester containing TiO2 nanoparticles are interesting biomimetic constructs for improved tissue regeneration. [source] Linking the flame-retardant mechanisms of an ethylene-acrylate copolymer, chalk and silicone elastomer system with its intumescent behaviourFIRE AND MATERIALS, Issue 6 2005Anna Hermansson Abstract In this paper the flame-retardant mechanisms of a flame-retardant system consisting of ethylene-acrylate copolymer, chalk and silicone elastomer are linked to its foaming process and to its formation of a final intumescent structure. Thermocouples were placed inside and at the surface of cone calorimeter test specimens in order to measure the temperature at different depths during the formation of the intumescent structure. The temperature and visual observations of the foaming process were then linked to chemical reactions seen with thermogravimetric analysis and also coupled with earlier knowledge of the flame-retardant mechanism. A correlation is seen between the chemical reactions, the temperature (inside and at the surface of a cone calorimeter test specimen) as measured by thermocouples and visual observations in the intumescent process. Further, the outcome of this study provides useful information for achieving a deeper understanding of the flame-retardant mechanisms of the ethylene-acrylate copolymer, chalk and silicone elastomer system. Copyright © 2005 John Wiley & Sons, Ltd. [source] Development of heat shrinkable and flame-retardant EVA/CSM blendsFIRE AND MATERIALS, Issue 5 2001S. Ray Chowdhury A plastic (EVA) was blended with elastomer (CSM) with and without curatives. The elastomer phase (amorphous) contributed markedly to the shrinkability and most important is, took up a major amount of additive flame-retarding agent thus not affecting much the heat shrinkability of the plastic i.e. as a whole the blend. When the elastomer phase was crosslinked the flame-retardancy, due to a reduction of combustible volatile product, was increased. Additive flame-retardants hamper the heat-shrinkability of the blend to some extent depending on various factors such as blend composition, temperature, curing etc. The depression of shrinkability in the presence of flame-retarding agent was less for the cured sample and elastomer-rich blend compared with the uncured and plastic-rich blend, respectively. It was found that with an increase in the cure time and elastomer content the shrinkability as well as flame-retardancy was increased. At high temperature the sacrifice of the shrinkability in the presence of flame-retardants increased, for a particular blend. The shrinkability and flame-retardancy of a cured sample was higher than that of an uncured sample. The highest flame-retardancy was obtained in the presence of Sb2O3/Chlorohor. Copyright © 2002 John Wiley & Sons, Ltd. [source] The Irish sea trout enhancement programme: an assessment of the parr stocking programme into the Burrishoole catchmentFISHERIES MANAGEMENT & ECOLOGY, Issue 6 2002C. J. BYRNE The success of the sea trout, Salmo trutta L., enhancement programme carried out in the Burrishoole catchment in the west of Ireland from 1993 until 1998 is reviewed in terms of the number of fish stocked, the number of fish which migrated to sea and the number which returned from sea during this period. The success of the programme is also evaluated in terms of the cost of producing parr for stocking and the subsequent value of returning post-smolts (0+ sea age) and rod caught fish. A total of 49 235 tagged fish were released into Lough Feeagh, between 1993 and 1998. Of these fish, 14 788 were microtagged and the remainder, 34 447 had either elastomer or alphanumeric visible implant (VI) tags. Tag loss rates at release varied from 3 to 5.7%. Over the course of the programme a maximum of 7801 fish migrated through the traps towards sea, of which 581, or 7.4%, returned. In any 1 yr a maximum 13.1% of fish returned from sea. The average cost of producing a parr for stocking out was ,1.15, which translated into average values of ,8.16 per smolt and ,169 per returning post-smolt. [source] Advances and Applications of Biodegradable Elastomers in Regenerative MedicineADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Maria Concepcion Serrano Abstract When elastomers were first proposed as useful materials for regenerative medicine a few decades ago, their high versatility and suitability for a diverse and wide range of in vivo applications could not have been predicted. Due to their ability to recover after deformation, these materials were first introduced in tissue engineering in an attempt to mimic the mechanical properties of the extracellular matrix. Furthermore, elastomeric characteristics have been described as important criteria for cell interaction by modulating cellular behavior. From soft to hard tissues, elastomers have demonstrated degradation, mechanical, and biocompatibility requirements in accordance with the target tissue. In this feature article, biodegradable synthetic polyester elastomers that have been reported in the literature are discussed, with special focus on those that show promise for in vivo tissue replacement. Their satisfactory performance in vivo shows the promise of elastomers for use in regenerative medicine. However, further investigation is required to demonstrate the prospect of elastomer-based therapies in clinical trials. [source] Reversibly Deformable and Mechanically Tunable Fluidic AntennasADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Ju-Hee So Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ,90% efficiency over a broad frequency range (1910,1990,MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1,0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna. [source] Metal Ion Implantation for the Fabrication of Stretchable Electrodes on ElastomersADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Samuel Rosset Abstract Here, the use of low-energy metal ion implantation by filtered cathodic vacuum arc to create highly deformable electrodes on polydimethylsiloxane (PDMS) membranes is reported. Implantation leads to the creation of nanometer-size clusters in the first 50,nm below the surface. When the elastomer is stretched, these small clusters can move relative to one another, maintaining electrical conduction at strains of up to 175%. Sheet resistance versus ion dose, resistance versus strain, time stability of the resistance, and the impact of implantation on the elastomer's Young's modulus are investigated for gold, palladium, and titanium implantations. Of the three tested metals, gold has the best performance, combining low and stable surface resistance, very high strain capabilities before loss of electrical conduction, and low impact on the Young's modulus of the PDMS membrane. These electrodes are cyclically strained to 30% for more than 105 cycles and remain conductive. In contrast, sputtered or evaporate metals films cease to conduct at strains of order 3%. Additionally, metal ion implantation allows for creating semi-transparent electrodes. The optical transmission through 25-µm-thick PDMS membranes decreases from 90% to 60% for Pd implantations at doses used to make stretchable electrodes. The implantation technique presented here allows the rapid production of reliable stretchable electrodes for a number of applications, including dielectric elastomer actuators and foldable or rollable electronics. [source] Silicone,Poly(hexylthiophene) Blends as Elastomers with Enhanced Electromechanical Transduction Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2008F. Carpi Abstract Dielectric elastomers are progressively emerging as one of the best-performing classes of electroactive polymers for electromechanical transduction. They are used for actuation devices driven by the so-called Maxwell stress effect. At present, the need for high-driving electric fields limits the use of these transduction materials in some areas of potential application, especially in the case of biomedical disciplines. A reduction of the driving fields may be achieved with new elastomers offering intrinsically superior electromechanical properties. So far, most attempts in this direction have been focused on the development of composites between elastomer matrixes and high-permittivity ceramic fillers, yielding limited results. In this work, a different approach was adopted for increasing the electromechanical response of a common type of dielectric elastomer. The technique consisted in blending, rather than loading, the elastomer (poly(dimethylsiloxane)) with a highly polarizable conjugated polymer (undoped poly(3-hexylthiophene)). The resulting material was characterised by dielectric spectroscopy, scanning electron microscopy, tensile mechanical analysis, and electromechanical transduction tests. Very low percentages (1,6 wt %) of poly(3-hexylthiophene) yielded both an increase of the relative dielectric permittivity and an unexpected reduction of the tensile elastic modulus. Both these factors synergetically contributed to a remarkable increase of the electromechanical response, which reached a maximum at 1 wt % content of conjugated polymer. Estimations based on a simple linear model were compared with the experimental electromechanical data and a good agreement was found up to 1 wt %. This approach may lead to the development of new types of materials suitable for several types of applications requiring elastomers with improved electromechanical properties. [source] A Continuous Flow Synthesis of Micrometer-Sized Actuators from Liquid Crystalline ElastomersADVANCED MATERIALS, Issue 47 2009Christian Ohm We demonstrate the use of a microfluidic setup to prepare monodisperse and spherical beads from a liquid crystalline elastomer. These particles show a strong and reversible shape change into a cigar-like conformation during the transition into the isotropic phase. These properies are a result of the monodomainic alignment of the mesogens in the flow field of the microfluidic setup. [source] Vertically Aligned Nanowires on Flexible Silicone using a Supported Alumina Template prepared by Pulsed AnodizationADVANCED MATERIALS, Issue 40 2009Stefan Mátéfi-Tempfli Carpets of vertically aligned nanowires on flexible substrates are successfully realized by a template method. Applying special pulsed anodization conditions, defect-free nanoporous alumina structures supported on polydimethylsiloxane (PDMS), a flexible silicone elastomer, are created. By using this template with nanopores ending on a conducting underlayer, a high-density nanowire array can be simply grown by direct DC-electrodeposition on the top of the silicone rubber. [source] Biomedical Materials: Nanoporous Biodegradable Elastomers (Adv. Mater.ADVANCED MATERIALS, Issue 2 20092/2009) The mechanical properties and degradation rate of elastomers can be tailored with nanoporosity. The elastomers described in this study by Guillermo Ameer and co-workers (p. 188) are based on citric acid and are biocompatible. The nanopores also facilitate the entrapment and slow release of macromolecular therapeutics. The inside cover depicts the nano- and microarchitecture of the elastomer prior to pore collapse. [source] Structure and properties of cross-linked polyurethane copolymersADVANCES IN POLYMER TECHNOLOGY, Issue 3 2009S. Oprea Abstract Polyurethane elastomers based on polyester diols and aromatic or aliphatic diisocyanates can be used as vibration dampers and isolation materials. Two series of cross-linked polyurethanes with various hard segment structures and different amounts were prepared and thermomechanical properties of these materials were studied. Cross-linked polyurethane copolymers composed of poly(ethylene adipate)diol as soft segment and 4,4,-methylenebis(phenylisocyanate), 1,6-hexamethylene diisocyanate, and diols glycerin, 1,4-butanediol, and 1,6-hexanediol as hard segments were synthesized by a two-step process. The networks have been prepared by end-linking a mixture of the bifunctional precursor chains with trifunctional cross-linkers at off-stoichiometric ratios. The results show that the cross-link and the polyurethane hard segment interaction play a special role in the interconnected chain density and its magnitude is revealed by the mechanical properties. Of most importance, maximum stress, tensile modulus, and elongation at break increased significantly at the 22 wt % composition of hard segment content. Interchain cross-linking improves thermal stability, which was measured by thermogravimetric analysis and differential scanning calorimetry. Cross-linked polyurethane behaves as an elastomer and is useful for shock, noise, and vibration control. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:165,172, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20155 [source] | ||||||||||||||||||||||||||||||||||